1. Field of the Invention
This invention relates to a neodymium-containing transparent resin and to a method for the manufacture of this resin. More particularly, this invention relates to a neodymium-containing transparent resin capable of selectively absorbing the light of wavelength ranges other than the wavelength ranges of the three primary colors and to a method for the manufacture of this resin.
2. Description of Prior Arts
On the inner surface of the panel glass of a color cathode-ray tube, phosphors which emit the three primary colors of red, green and blue are deposited in a pattern of a multiplicity of dots or stripes to form a fluorescent screen. A color picture image is observed through the panel glass by shooting the electron beams projected from electron guns toward the fluorescent screen through a shadow mask or an aperture grill.
When the picture image of the color cathode-ray tube is viewed through the panel glass, however, there is experienced a persistent problem that the external light existing about the viewer such as, for example, the solar light entering the room through a window or the light from interior lighting devices like fluorescent lamps impinges on the fluorescent screen and seriously impaired the contrast of the picture image composed of red, green and blue lights.
For the purpose of preventing the contrast from being impaired by the external light, there has heretofore prevailed the practice of incorporating minute amounts of NiO and CoO in the panel glass thereby imparting a neutral gray color to the glass and lowering the lightness of the glass. Since the glass of neutral gray color exhibits substantially uniform transmittance over the entire wavelength range of visible light including those of the emission spectra of red, green and blue, however, the attempt to lower the transmittance of this gray glass for the purpose of improving the contrast entails a disadvantage that the glass also absorbs the lights of red, green and blue emitted from the phosphors and degrades the luminance of the picture image.
The emission spectra of a certain set of phosphors are as shown in FIG. 1. From this diagram, it can be expected that the picture image will be allowed to retain its high luminance and curb loss of contrast by conferring upon the panel glass an ability to pass fully the colors of wavelengths corresponding to the fluorescence spectra of red (curve A), green (curve B) and blue (curve C) and absorb fully the light excluding the colors of such wavelengths and readily perceived by human eyes such as, for example, the light of yellow color. It can also be expected that, by properly selecting an absorption wavelength range, the colors of specific undesirable wavelengths will be selectively removed by absorption from the aforementioned emission spectrum and, consequently, the color emitted from the phosphor will be improved in purity and the color reproduction in the color image will be proportionately enhanced. It is, however, extremely difficult to attain such purposes by directly improving the panel glass. If direct improvement of the panel glass is managed to be carried through, it will prove highly expensive.
One of the solutions of this problem is a use of transparent resin containing neodymium as, for example, a front panel for the cathode-ray tube. As neodymium-containing resins, there have been proposed (1) a resin composition formed by incorporating an inorganic neodymium compound such as, for example, neodymium phosphate, neodymium carbonate, neodymium sulfate, neodymium oxide, or neodymium nitrate into a synthetic resin (Japanese Patent Kokai No. 56851/1976) and (2) a resin composition formed by incorporating an organic neodymium compound such as, for example, neodymium ethylenediaminetetraacetate, neodymium acetate or neodymium stearate into a synthetic resin such as methyl methacrylate resin or styrene resin (Japanese Patent Kokai No. 58444/1976).
The former resin composition, however, has had a disadvantage that since the neodymium compound used therein is an inorganic substance and shows no sufficient compatibility to the organic synthetic resin such as methyl methacrylate resin or styrene resin, it is not easily dispersed uniformly in the resin when it is kneaded with the resin. The latter resin composition, too, has had a disadvantage that although the neodymium compound used therein is an organic substance, it is not easily dispersed uniformly when it is kneaded with the methyl methacrylate resin which is solid and, therefore, has been melted by heating before the kneading, with the result that the produced resin composition lacks transparency and consequently exhibits insufficient total and parallel light transmittance and even produces haze. It has long been known to the art that the aforementioned organic neodymium compounds including neodymium acetate, for example, exhibit poor compatibility to methyl methacrylate resin. To cope with this drawback, there has been proposed a method which comprises causing a given neodymium salt to be dissolved intimately with methyl methacrylate through the agency of anhydrous stannic chloride as a solvent and cast molding the resultant composition by polymerization (Japanese Patent Publication No. 5091/1969). This method proves expensive because it effects the cast polymerization of the composition in the presence of stannic chloride as the solvent. Moreover, the produced resin does not readily acquire thorough transparency because of the cloudiness due to dispersion of fine particles therein. It also shows insufficient weatherability and tends to be readily deprived of transparency.
It is, therefore, an object of this invention to provide a neodymium-containing transparent resin and a method for the manufacture of this resin.
Another object of this invention is to provide a neodymium-containing transparent resin capable of selectively adsorbing the portion of light of wavelengths excluding the wavelengths of the three primary colors and, therefore, advantageously useful as optical resin material and a method for the manufacture of this resin.